Question

Describe different types of ovules. Draw their labelled diagrams.

Accepted Answer

The ovule is the megasporangium of the angiosperms, located within the ovary. A small thin tube-like apical portion of the ovule remains uncovered is called micropyle. The basal part of the ovule opposite the micropyle is known as chalaza.

There are different types of ovules present in angiosperms. On the basis of the relative position of micropyle and chalaza, mature ovules are classified into six types:

i) Orthotropous ovule: When micropyle, chalaza and funicle lie in a straight line, such type of ovule is known as orthotropous ovule. This type of ovule is erect or vertical. Examples: plants of Polygonaceae, Piperaceae etc.

ii) Anatropous Ovule: In this type of ovule, due to the unilateral growth of funicle, it is inverted by rotation of 180⁰. Therefore, the micropyle comes near the hilum and the micropyle and chalaza remain in a straight line. It is the common type of ovule in angiosperms.

iii) Campylotropous Ovule: In this, due to the curvature of the ovule, the chalaza lies at the right angle to the micropyle. Both the nucellus and embryo sac become horse-shoe shaped. Examples: plants of Brassicaceae.

iv) Amphitropous or Transverse Ovule: In this type of ovule, nucellus, micropyle and chalaza lie at right angle to the funicle and due to curvature of ovule the embryo sac get curved.

v) Hemianatropous Ovule: When micropyle and chalaza lie in a horizontal line and the funicle is present at right angle to these, the ovules are called hemianatropous types.

vi) Circinotropous Ovule: In this type of ovule, the funicle is excessively elongated and the entire ovule remains rotated at 360 $°$ . The funicle covers the entire ovule and it remains attached to the ovule at one point only.

	List - I		List - II
(a)	Calyx	(i)	$\oplus$
(b)	Ovary superior	(ii)	$%$
(c)	Actinomorphic	(iii)	$C$
(d)	Zygomorphic	(iv)	$K$
		(v)	$G$

Describe different types of ovules. Draw their labelled diagrams.

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